Thermoplastic throttle body

ABSTRACT

The invention relates to a process of making a throttle body comprising injection-moulding of a reinforced thermoplastic composition, wherein a polyethylene terephthalate composition containing a nucleating agent and 25-60 mass % of glass-fibres is used as the reinforced thermoplastic composition. Advantages of the throttle body obtainable by the process according to the invention include excellent dimensional tolerances and stability, significant weight reduction of the body, and improved fuel efficiency of an internal combustion engine equipped with an air-intake assembly comprising a throttle body according to the invention.

[0001] The invention relates to a process of making a throttle body foruse in an air-intake assembly of an internal combustion engine,comprising injection moulding of a reinforced thermoplastic composition.The invention also relates to a throttle body comprising at least ahousing made of a specific thermoplastic composition, and to anair-intake assembly, comprising such a throttle body.

[0002] Such a process is known from EP 0926336 A2. In this publication athrottle body is formed from a reinforced thermoplastic material havinga high (e.g. greater than 40%) glass/mineral content, which can sustaincontinuous high temperatures of 125° C., is chemically resistant tocommon automotive fluids, is generally non-hydrophobic with waterabsorption rates less than about 1.5%, is dimensionally stable, and ispreferably of lower cost and lighter than metals. Preferably,polybutylene terephthalate or polyphenylene sulphide is employed as thethermoplastic material.

[0003] Conventionally, a throttle body and an air-intake manifold, asparts of an air-intake assembly, were made from metals such as aluminiumor steel. Such metal components are generally heavier and costlier thandesirable. Consequently, plastic materials have been evaluated for theirpotential to offer both cost and performance benefits. But while plasticair-intake manifolds have come widely into use, throttle bodies aregenerally still made of metal.

[0004] A drawback of the thermoplastic throttle body known from EP0926336 A2 is its insufficient dimensional tolerance and stability.Dimensional tolerances and stability are essential properties in thisapplication, because even very small differences in dimensions betweenthrottle bodies produced in a series, or minor dimensional changes in athrottle body as a result of for example changing environmentalconditions during use may hamper accurate metering of air flow duringengine operation, or induce leaks in connections between the throttlebody and air-intake manifold or air-duct to air-cleaner.

[0005] The object of the invention is therefore to provide a process formaking a thermoplastic throttle body, which throttle body does not, orat least to a much lesser extent, show these disadvantages.

[0006] This object is achieved with a process wherein the throttle bodyis injection-moulded from a polyethylene terephthalate compositioncontaining a nucleating agent and 25-60 mass % of glass-fibres as thereinforced thermoplastic composition.

[0007] It is surprising that the process according to the inventionsolves said problem, because polyethylene terephthalate compositions areknown to be more difficult to injection-mould than e.g. polybutyleneterephthalate compositions.

[0008] Another advantage of the process according to the invention isthat it allows more design freedom than when making a throttle body froma metal. In case a throttle body design is used that is similar to apart made from metal, the present process allows a significant weightreduction, for example of about 60%. Another advantage is that a partcan be moulded with a very good and smooth surface appearance. Asurprising and important advantage of the throttle body obtainable bythe process according to the invention is that a significant reductionin fuel-consumption is possible for a passenger car in which theair-intake assembly comprises a throttle body according to theinvention.

[0009] The effect of the invention is already obtained with a throttlebody comprising at least a housing that is moulded from the polyethyleneterephthalate composition, and other components of the throttle body,like a valve element and shaft for selectively controlling the airflowto the air-intake manifold, made from other materials, like a metal.More preferably, the throttle body housing and the valve element aremade from a polyethylene terephthalate composition, most preferably fromthe same polyethylene terephthalate composition, optionally containing alubricant. The advantages thereof include lower manufacturing costs,reduced wear between the parts and more accurate operation underchanging environmental conditions. Different designs or types ofthrottle housing bodies and valve elements may be used, including aconventional housing in which a butterfly-type valve is rotatablymounted. An advantage of using the polyethylene terephthalatecomposition is that also relatively thin moulded parts still show highstrength and stiffness.

[0010] The polyethylene terephthalate composition that is used in theprocess according to the invention contains as a matrix polymer apolyethylene terephthalate polymer, i.e. a polyester based onterephthalic acid or an ester thereof and ethylene glycol as mainmonomers. The polyethylene terephthalate can also contain small amountsof other diacids, like isophtalic acid, or other diols, like diethyleneglycol as comonomers. Preferably the composition contains at least apolyethylene terephthalate homopolymer. A polyethylene terephthalatehomopolymer is herein understood to contain less than 5 mole % ofmonomers other than terephthalic acid or an ester thereof and ethyleneglycol. The advantage of such a homopolymer is a higher melting pointand better crystallisation behaviour. More preferably the polyethyleneterephthalate contains less than 4 mol %, even more preferably less than3 mol % and most preferably less than 2 mol % of comonomer. Preferablyat least 50 mass % of polyethylene terephthalate in the composition is ahomopolymer, most preferably at least 75 mass %. The composition mayfurther contain a polyethylene terephthalate copolymer containing morethan 5 mole % of other monomers, like the type of polymer used formaking bottles. Such polymers may be used as virgin grades, but also asrecycled grades, that is material recovered from post-use products, e.g.soft-drink bottles.

[0011] As a nucleating agent in the polyethylene terephthalatecomposition that is used in the process according to the invention, anyknown nucleating agents can be used. Preferably, an inorganic additivelike micro-talcum, or a metal-carboxylate, especially analkalimetal-carboxylate like sodium benzoate is used. More preferably,an alkalimetal-carboxylate like sodium benzoate is used in an amount offrom about 0.05 to 0.5 mass % (based on polyethylene terephthalate).

[0012] Suitable glass fibres for use as reinforcing agent in thepolyethylene terephthalate composition that is used in the processaccording to the invention generally have a fibre diameter of from 5 to20 μm, preferably 8-15 μm, and most preferably 9-11 μm for optimalbalance of mechanical properties, like stiffness, strength andtoughness, and processability. The glass fibres have a sizing on theirsurface that is compatible with thermoplastic polyesters and generallycontains an epoxy- or amino-functional compound. Preferably the sizingcontains an epoxy-functional compound. The advantage thereof is a gooddispersability in polyethylene terephthalate and improved long-termmechanical properties of the polyethylene terephthalate composition,especially improved fatigue behaviour.

[0013] In a preferred embodiment of the process according to theinvention, the polyethylene terephthalate composition contains 28-50mass % of glass fibres, more preferably 30-45 mass % of glass fibres,and even more preferably 33-38 mass % glass fibres. The advantage hereofis a more balanced compromise between high strength and stiffness, a lowrelative density and easy processing behaviour of the polyethyleneterephthalate composition.

[0014] In a special embodiment of the process according to theinvention, the polyethylene terephthalate composition has an averageglass content of between 25 and 60 mass %, which average glass contentshows a standard deviation of not more than 0.6% between different lotsand between samples taken from one lot of polyethylene terephthalatecompositions, and thus also between different parts moulded from thesecompositions. Typical lot sizes as produced are from about 5000 to 25000kg. Preferably this standard deviation is not more than 0.5%, morepreferably not more than 0.4%, and most preferably not more than 0.3%.The inventors found that a process in which a polyethylene terephthalatecomposition with such narrow distributions in the glass fibres contentis used, a very good performance in dimensional tolerances of throttlebodies is obtained. In addition to enabling a constant and reproduciblerelative density of the composition and products moulded thereof, littlevariation in glass fibres content probably also results in littlefluctuation in melt viscosity of the composition, and thus in a verystable injection moulding process, i.e. in little fluctuations inpressures, temperatures etc. This is not only advantageous forminimising degradation of the polyethylene terephthalate compositionduring the moulding process, but also for controlling crystallinity,density, dimensions and residual stresses of the moulded part obtained.

[0015] Generally the polyethylene terephthalate in the polyethyleneterephthalate composition has a relative solution viscosity (RSV,determined on a solution of 1 gram polymer in 125 grams of a 7/10 (m/m)trichlorophenol/phenol mixture at 25° C.; method based on ISO 1628-5) offrom 1.50 to 2.00, preferably 1.55-1.90, more preferably 1.60-1.85, andmost preferably 1.65-1.80. In general, a higher RSV will result inimproved strength and toughness of a moulded composition, whereas alower RSV promotes melt flow and crystallisation speed of a composition.With the present RSV range an optimum in performance is reached, withoutthe need for adding impact-modifiers or flow-promoters. In order toarrive at these RSV values, the polyethylene terephthalate compositionmay have been post-condensed in the solid state after mixing the variouscomponents of the composition, for example by exposing the compositionin granular form to an elevated temperature of up to about 10° C. belowits melting point, in an inert atmosphere during several hours. Anotheradvantage of such a solid state post-condensation is that any volatilespresent in the composition, and that may affect processing behaviour ofthe composition or properties of a part moulded thereof, aresubstantially removed.

[0016] The polyethylene terephthalate composition that is used in theprocess according to the invention is preferably substantially free ofplasticizers, i.e. it preferably contains no additives that lower glasstransition temperature and therewith the temperature range in whichcrystallisation from the melt occurs. The advantage hereof is that alsoduring continuous use at elevated temperature the properties of aninjection-moulded part will not change due to loss of plasticizer.

[0017] As a consequence of the absence of plasticizers, the polyethyleneterephthalate composition is preferably injection-moulded into a mouldthat is kept constant at a relatively high temperature, of up to about170° C., in order to obtain moulded parts of high crystallinity andexcellent dimensional stability. Because of practical and technicalconsiderations a lower mould temperature would be preferred. In theprocess according to the invention, the mould is therefore preferablyheated at a temperature between 110 and 170° C., more preferably at125-160° C., even more preferably at 130-150° C., and most preferably at135-145° C.

[0018] The polyethylene terephthalate composition that is used in theprocess according to the invention may also contain 0-20 mass % of otherfibrous or particulate mineral fillers. Preferably filler particles areused, for example talcum or kaolin, because they contribute to thestiffness of the composition without undesirably enhancing anisotropy inproperties of the composition.

[0019] The polyethylene terephthalate composition that is used in theprocess according to the invention can also contain minor amounts ofusual additives, like stabilisers and anti-oxidants, colorants,processing aids like a mould-release agent, viscosity-modifiers like achain extension agent, impact-modifiers, lubricants, etcetera. Examplesof suitable impact-modifiers include rubbery olefinic copolymersfunctionalised with reactive groups, for example with epoxy-groups;copolymers of olefins and (meth)acrylates, eg. ethylene/acrylic acidcopolymers, that may optionally be partly neutralized; or polyesterelastomers like a polyether ester block-copolymer. Suitable examples oflubricants or wear- and friction-reducing agents include fluorinatedhydrocarbons like poly(tetrafluoro ethylene), graphite, or molybdenumdisulfide.

[0020] The polyethylene terephthalate composition that is used in theprocess according to the invention can be made by mixing the variouscomponents using processes well known to the skilled person. Suitablemixing equipment includes a twin-screw compounding extruder to which thevarious components are metered separately or as a pre-blend. The moltenmixture is extruded into a strand and granulated. The granulate may beused as such after drying, or undergo an additional post-condensationstep in the solid phase in order to increase its viscosity.

[0021] In a most preferred embodiment of the process according to theinvention a polyethylene terephthalate composition containing 0.05-0.5mass % (based on polyethylene terephthalate) of sodium benzoate as anucleating agent, 35 mass % of glass fibres, and with a RSV of 1.60-1.85is injection-moulded into a mould that is kept at 1135-145° C. Theadvantage is that a throttle body is obtained that shows very gooddimensional tolerances and stability, high mechanical strength andstiffness, excellent fatigue behaviour at a temperature range of −40 upto over 100° C., and very good chemical and wear resistance.

[0022] The invention also relates to a throttle body for use in anair-intake assembly of an internal combustion engine, comprising atleast a housing that is injection-moulded from a polyethyleneterephthalate composition containing a nucleating agent and 25-60 mass %of glass-fibres. This novel throttle body shows advantageous propertiesas described above. Preferably, the main components of the throttlebody, at least the housing and the valve element, are moulded from saidcomposition.

[0023] The invention also relates to a throttle body for use in anair-intake assembly of an internal combustion engine, comprising atleast a housing, obtainable by the process according to the invention.Injection moulding of said polyethylene terephthalate compositionaccording to the process according to the invention has the advantagethat the moulded products show very high consistency in performance.More preferably the main components of the throttle body are obtainableby the process according to the invention, i.e. at least the throttlebody housing and its valve element.

[0024] The invention also relates to an air-intake assembly of aninternal combustion engine, comprising a throttle body according to theinvention. The advantage thereof is a better-balanced assembly ofair-duct, throttle body and air-intake manifold, because of the lowermass of the throttle body. In addition, a car equipped with saidair-intake assembly is found to show improved fuel efficiency.Preferably the air-duct and air-intake manifold are also made from athermoplastic composition. The air-duct can be made from a polyamide,for example a polyamide 6 (PA 6), PA 66, or PA 46 composition, or from ablock-copolyester composition, for example based on a segmentedpolyether ester block-copolymer. The air-intake manifold is generallymade from a glass fibre reinforced polyamide, for example PA 6, PA 66,or PA 46 composition. It has been found that such an all-thermoplasticair-intake assembly shows less vibrational motions during use in a car,thereby resulting in an improved airflow.

[0025] The invention will now be further elucidated with reference tothe following example.

EXAMPLE

[0026] A conventional throttle body housing design, which was normallymade in aluminium, was slightly modified to accommodate for the use of apolyethylene terephthalate composition. Considering the lower thermalconductivity of such a polyethylene terephthalate composition versusmetal, a cooling channel could for example be omitted. Aninjection-moulding tool was made, mounted in an injection-mouldingmachine, and heated at a constant temperature of 140° C. With cylindertemperature settings of 285-280-280-285° C. (from hopper to nozzle) anucleated polyethylene terephthalate composition based on a polyethyleneterephthalate homopolymer containing 0.15 mass % (based on polyethyleneterephthalate) of sodium benzoate, reinforced with 35 mass % (based onthe composition) of glass fibres of 10 μm diameter and with anepoxy-compound containing sizing system, Arnite® AV2 370/B of DSMEngineering Plastics (NL), which was previously dried to a water contentof less than 0.03 mass %, was processed. The RSV amounted 1.73 (asdetermined on a solution of 1 gram polymer in 125 grams of a 7/10 (m/m)trichlorophenol/phenol mixture at 25° C.). Subsequently other componentswere mounted to the housing thus obtained. The weight of thisthermoplastic throttle body amounted 190 grams, versus 460 grams for theoriginal metal body. A weight reduction of about 60% was thus alreadyobtained without optimising the housing design to the specificproperties of the composition used.

[0027] The obtained throttle body was mounted between an air-duct and anair-intake manifold in a passenger car, and subjected to a standard testprotocol. It was, amongst others, observed that the air pressure in theair-intake manifold was about 26.2 MPa versus 26.8 MPa for a controlexperiment with a conventional assembly without the throttle bodyaccording to the invention. The average distance driven on one litre offuel in the present testing was 19.0 km/litre, whereas in the controlexperiment with a conventional assembly without the throttle bodyaccording to the invention average distance amounted 17.0 km/litre. Thismeans a reduction in fuel consumption of almost 10% was realized, evenwithout optimising the design of the throttle body and its componentslike the housing to the specific material and processing characteristicsof the polyethylene terephthalate composition used.

1. Process of making a throttle body comprising injection-moulding of areinforced thermoplastic composition, characterised in that apolyethylene terephthalate composition containing a nucleating agent and25-60 mass % of glass-fibres is used as the reinforced thermoplasticcomposition.
 2. Process according to claim 1, wherein a throttle bodyhousing is injection-moulded from the polyethylene terephthalatecomposition.
 3. Process according to claim 1, wherein a throttle bodyhousing and a valve element are injection-moulded from the samepolyethylene terephthalate composition.
 4. Process according to any oneof the claims 1-3, wherein the polyethylene terephthalate compositioncontains at least a polyethylene terephthalate homopolymer.
 5. Processaccording to any one of the claims 1-4, wherein the polyethyleneterephthalate composition contains 30-45 mass % of glass fibres. 6.Process according to claim 5, wherein the polyethylene terephthalatecomposition contains 33-38 mass % of glass fibres.
 7. Process accordingto any one of the claims 1-6, wherein the polyethylene terephthalatecomposition has a relative solution viscosity of 1.60-1.85.
 8. Processaccording to any one of the claims 1-7, wherein the polyethyleneterephthalate composition is substantially free of plasticizers. 9.Process according to any one of the claims 1-8, wherein the polyethyleneterephthalate composition is injected into a mould that is heated at135-145° C.
 10. Throttle body for use in an air-intake assembly of aninternal combustion engine, comprising at least a housing that isinjection-moulded from a polyethylene terephthalate compositioncontaining a nucleating agent and 25-60 mass % of glass-fibres. 11.Air-intake assembly of an internal combustion engine, comprising athrottle body according to claim 10.